1. Field of the Invention
The present invention relates to a method for treating a support or substrate for an electrophotographic photosensitive member comprising a substrate having thereon a non-monocrystalline film containing at least a silicon atom and a hydrogen atom. The present invention also relates to a method for manufacturing an electrophotographic photosensitive member, making use of the method for treatment of such a support or substrate. More particularly, the present invention is concerned with a method for treating a substrate for an electrophotographic photosensitive member comprising a metallic substrate having thereon a non-monocrystalline deposited film containing a silicon atom and a hydrogen atom, formed by plasma CVD, and is also concerned with a method for manufacturing an electrophotographic photosensitive member, making use of the method for treating such a substrate.
2. Related Background Art
As photosensitive materials used in electrophotographic photosensitive members, non-monocrystalline deposited films have been proposed, as exemplified by amorphous deposited films comprising an amorphous silicon or the like compensated with hydrogen and/or a halogen such as fluorine or chlorine, some of which have been put into practical use.
As processes for forming such deposited films, a number of processes are conventionally known, as exemplified by sputtering, thermal CVD (a process in which a starting material gas is decomposed by heat), optical CVD (a process in which a starting material gas is decomposed by light), and plasma CVD (a process in which a starting material gas is decomposed by plasma). In particular, plasma CVD, i.e., a process in which a starting material gas is decomposed by direct current, high-frequency or microwave glow discharge to form a thin-film member deposited film on a substrate is most suited for the process for forming an amorphous-silicon deposited film used in electrophotography. This process has been put into practical use or is being more and more improved.
For example, Japanese Patent Application Laid-open No. 54-86341 discloses an example of such an amorphous silicon photosensitive member.
This amorphous silicon photosensitive member can be free from environmental pollution, and is characteristic of a high image quality and a high durability. Amorphous silicon photosensitive members presently put into practical use well have such characteristic features. However, in order for the amorphous silicon photosensitive members to become more and more widespread, it is sought to reduce cost, to improve electrical characteristics, and also to enhance durability.
In recent years, global environmental pollution has also been questioned, and now improvements must be urgently made on not only elimination of what may result in environmental pollution but also in the manner of handling something harmful at the stage of manufacture. Although the amorphous silicon photosensitive members are free from any environmental pollution in themselves, review has become necessary from such a viewpoint on various matters including the cleaning of cylinders which are substrates of photosensitive members and even the packaging of products after the manufacture.
Incidentally, glass, quartz, silicon wafer, heat-resistant synthetic resin film, stainless steel, aluminum, etc. have been proposed as materials for the substrate on which the non-monocrystalline film comprising an amorphous silicon film or the like is formed. Of these materials, as materials for the substrate on which the amorphous silicon photosensitive material is deposited, metals are used in many instances so that the substrate can endure the electrophotographic process comprising charging, exposure, development, transfer and cleaning and also because positional precision can be maintained at a high level so as to prevent lowering of image quality. As such metals, aluminum alloys are widely used and have, in particular, a superior workability, dimensional stability, etc.
For example, Japanese Patent Application Laid-open No. 59-193463 describing a technique relating to the materials for substrates of electrophotographic photosensitive members making use of amorphous silicon, discloses a technique in which the substrate comprises an aluminum alloy with an Fe content of not more than 2,000 ppm and by which an electrophotographic photosensitive member that can give a good image quality can be obtained.
This publication discloses a procedure comprising cutting a cylindrical (or cylinder-like) substrate by means of a lathe, and mirror-finishing the surface, followed by glow discharging to form an amorphous silicon film. In general, when the substrate is worked in this way, it is lathed using an oily substance such as cutting oil. Hence, a residue of the oily substance always remains on the substrate having been worked, and also cutting scrap produced during working, dust in the air, etc. adhere to the substrate. If these residues remain thereon because of insufficient cleaning, a fault-free, uniform deposited film can not be formed, and satisfactory electrical characteristics can not be obtained. These residues cause a defective image particularly when the substrate is used for a long period of time. Such problems are known to occur. Accordingly, the substrate must be well cleaned with a great care when electrophotographic photosensitive members are manufactured.
Under such circumstances, for example, Japanese Patent Application Laid-open No. 61-171798 discloses a technique relating to a method of working substrates for electrophotographic photosensitive members. This publication discloses a technique in which a substrate is cut using a cutting oil composed of specific components to give an electrophotographic photosensitive member comprising amorphous silicon of a good quality. This publication also discloses that the substrate is cleaned with triethane (herein referred to as trichloroethane: C.sub.2 H.sub.3 Cl.sub.3) after cutting. The photosensitive members manufactured using the substrate cleaned by such a method can achieve a certain degree of performance, without causing any particular problems on performance, and are now in wide use.
Besides the cleaning method described above, the following method is employed as a cleaning method by which the oily substance and other deposits are removed after cutting of the substrate (mainly those made of aluminum alloy) for an electrophotographic photosensitive member.
(1) Ultrasonic cleaning using an organic solvent
A substrate is subject to ultrasonic cleaning in a hot medium bath, rinsing in a cold medium bath, completion of cleaning by vapor cleaning in a vapor bath, and drying. Optionally a hot medium bath may be further provided or a surfactant is added to the solvent.
The following are used as the solvent.
(i) Chlorine types: Trichloroethylene, perchloroethylene, methylene chloride, 1,1,1-trichloroethylene.
(ii) Fluorine types: Flon-113, Flon-112, other flon (chlorofluorohydrocarbon) mixed solvents.
(iii) Other types: Benzene, toluene, isopropyl alcohol, methanol, ethanol, acetone.
This method may achieve only a weak cleaning power and in particular, may give insufficient cleaning power against the aforesaid deposits in the case of substrates having been left for a long time after cutting, and also has the problem that the organic solvents are harmful to human bodies and may adversely affect the work environment depending on how they are used.
(2) Chemical cleaning using acid or alkali
(i) Acids: Sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, hydrofluoric acid, chromic acid (removal of scales, decomposition of oxides).
(ii) Alkalis: NaOH, NaCO.sub.3, NaHCO.sub.3, Na.sub.3 PO.sub.4, Na.sub.2 HPO.sub.4, Na.sub.4 P.sub.2 O.sub.7 (sodium pyrophosphate) (decomposition of proteins, degreasing action)
(iii) Peroxides: Hydrogen peroxide, sodium perborate (oxide decomposition action).
In this method, there is a possibility of the substrate surface being corroded which causes change of the surface state, sometimes resulting in a lowering of electrophotographic performance of photosensitive members. In particular, it may have a very bad influence upon a substrate with a mirror-finished surface. An attempt to avoid this problem tends to result in incomplete cleaning. The cleaning power also is susceptible to changes depending on the concentration of a cleaning solution and hence great care must be taken to the handling of the cleaning solution.
Nonetheless, in any or all the above cleaning methods, it is difficult to completely remove the aforesaid deposits adhered to the substrate, so that the deposits may often remain on the surface of the substrate. This deposits are presumed to cause a local change in electrophotographic performance to give the aforesaid defective image.
Such problems may occur not only in the substrates made of aluminum alloy but also any substrates made of nickel, iron or copper.
As stated above, the substrate must be so disposed that the surface stains due to the cutting oil are removed as far as possible so as not to have an adverse influence on the electrophotographic performances of photosensitive members and also not to bring about a decrease in yield in the manufacture of photosensitive members. The above cleaning methods, however, have been often unable to completely answer such requirements. Moreover, the organic solvents including halogenated hydrocarbon solvents have an undesirable influence not only on human bodies but also the global environment, and hence their use must be avoided as far as possible.
To solve these problems, in recent years, several proposals were made for a method of cleaning the substrate with water in place of the cleaning solution described above.
Techniques relating to the surface treatment of substrates for electrophotographic photosensitive members by the use of water are proposed in Japanese Patent Applications Laid-open No. 58-014841, No. 61-273551, No. 63-264764 and No. 1-130159.
Japanese Patent Applications Laid-open No. 58-014841 discloses a technique in which a natural oxide film on the surface of an aluminum substrate of a selenium photosensitive member is removed and thereafter the substrate is immersed in water kept at a temperature of 60.degree. C. or higher to give a uniform oxide film.
Japanese Patent Application Laid-open No. 61-273551 discloses a technique in which the substrate is pretreated by alkali cleaning, trichloroethylene cleaning, or ultraviolet irradiation cleaning using a mercury lamp, when an electrophotographic photosensitive member is manufactured using an aluminum substrate provided thereon with selenium or the like, though admittedly different from amorphous silicon, by vacuum deposition. It also discloses that liquid degreasing and pure-water cleaning are carried out as a pretreatment of the ultraviolet irradiation cleaning to remove fats and oils having adhered to the surface of a cylindrical substrate.
Japanese Patent Application Laid-open No. 63-264764 discloses a technique in which the substrate surface is roughened by a water jet, a technique different from cleaning.
Japanese Patent Application Laid-open No. 1-130159 discloses a technique in which the support or substrate of an electrophotographic photosensitive member is cleaned with a water jet. This publication discloses examples of a photosensitive member, which includes those comprising a selenium, organic photoconductor and, at the same time, those comprising amorphous silicon, suggesting that this cleaning technique can be also applied to the amorphous silicon photosensitive member. This publication, however, actually does not refer at all to the problem that occurs when a substrate for the amorphous silicon photosensitive member is cleaned with the water jet, in particular, the problem peculiar to the case when the photosensitive member is formed by plasma CVD.
Meanwhile, there has been steady progress in making higher quality amorphous silicon photosensitive members as a result of studies on layer configuration.
For example, Japanese Patent Application Laid-open No. 54-145540 discloses that superior electrophotographic performances, e.g., a high dark resistance and a good photosensitivity, can be attained when an amorphous silicon containing carbon in a concentration of from 0.1 to 30 atomic % as a chemical modifier is used in a photoconductive layer of an electrophotographic photosensitive member.
Japanese Patent Application Laid-open No. 57-119357 also discloses that an electrophotographic photosensitive member with superior performances can be obtained when carbon atoms are distributed in amorphous silicon film in a larger quantity on the side of the substrate.
These techniques are bringing about improvements in the performances of electrophotographic photosensitive members. Under existing circumstances, however, there is much room for further improvement.
In the first place, it is earnestly desired to decrease black-spot or white-spot faulty image, called dots. At present, to make image quality much higher, it is desired to reduce minute dots that have not been of much concern.
Analysis of the cause of the dots has been gained by daily progress, and some findings have been obtained. The dots are mostly caused by abnormal growth called spherical protuberances ascribable to dust or the like produced when amorphous silicon is deposited as a film. Besides, there is also what is called running dots that may increase as the running is continued, which are caused by scattering of toner or inclusion of paper dust into a separation zone electric assembly. In order to decrease the defective or faulty image caused by such problems, those who are engaged in the manufacture of photosensitive members must take measures for not only increasing cleanness of the inside of a deposited film forming apparatus but also increasing breakdown voltage of an amorphous silicon photosensitive member with approaches from an improvement in the method of forming deposited films or from the manufacturing process.
In recent years, electrophotographic photosensitive members are also desired to have a higher image quality and a higher function. For this reason, it is required to faithfully reproduce an original containing a halftone as in photographs, while achieving a decrease in nonuniform performance, in particular, nonuniformity of the halftone. In the case of full-color copying machines having come into wide use in recent years, this nonuniformity results in a delicate unevenness of colors which becomes visually clearly recognizable, and hence has become of great importance.
In addition, electrophotographic, photosensitive members are also desired which maintain a high image quality and a high sensitivity and have greatly improved running performance in every environment. The running performance, in which the amorphous silicon photosensitive member most excels, makes it unnecessary to change the photosensitive member for new one until the service life of a copying machine itself has come to an end. This allows us to regard the photosensitive member as not an article for consumption but a component part of the copying machine, and thus has brought about a prospect for a possibility of liberation from routine maintenance such as replacement of the photosensitive member. Now, further new products are sought which have a durability of the same level as, or higher level than, the copying machine itself, and such durability is sought to be more greatly improved. Under such demands, it has been hitherto difficult, and is still unsatisfactory, to attain both the charge performance and the prevention of smeared images at high levels and to greatly improve the durability in every environment.
In order to meet such demands, it is required under the existing circumstances to reconsider the whole process starting from the step of cleaning a conductive substrate up to the step of manufacturing an electrophotographic photosensitive member.
An example of the method for manufacturing an electrophotographic photosensitive member in the instance where an aluminum alloy cylinder is used as the substrate and triethane is used in cleaning can be specifically shown as follows.
To a precision cutting lathe (manufactured by Pneumo Precision Inc.) provided with an air damper, a diamond cutting tool (trade name: MIRACLE BITE; manufactured by Tokyo Diamond K. K.) is so set as to be at a rake angle of 5.degree. with respect to the center line of the cylinder. Next, the substrate is vacuum-chucked to the rotating flange of the lathe, and mirror cutting is carried out so as to give an outer diameter of 108 mm under conditions of a peripheral speed of 1,000 m/min and a feed rate of 0.01 mm/R, in combination with the spraying of white kerosene from attached nozzles with the vacuuming of cuttings through similarly attached nozzles.
Next, the substrate thus cut is cleaned with triethane to clean off the cutting oil and cuttings adhered to the surface.
Next, on this mirror-finished and cleaned substrate, a deposited film mainly composed of amorphous silicon is formed using an apparatus for forming a photoconductive member deposited film by glow discharge decomposition, as shown in FIG. 1.
In FIG. 1, a reaction vessel 101 is comprised of a base plate 102, a wall 103 and a top plate 104. Inside this reaction vessel 101, an electrode 105 (the cathode) is provided. A substrate 106 on which the amorphous silicon deposited film is formed is disposed at the center of the cathode 105 and serves also as the anode.
To form the amorphous silicon deposited film on the substrate 106 using this deposited film forming apparatus, firstly a starting material gas inlet valve 107 and a leak valve 108 are closed and an exhaust valve 109 is opened to evacuate the reaction vessel 101. At the time when a vacuum indicator points to about 5.times.10.sup.-6 torr, the starting material gas inlet valve 107 is opened to allow starting material gases as exemplified by SiH.sub.4 gas and other gas adjusted to a given mixing ratio in a mass flow controller 111, to flow into the reaction vessel. Then, after the surface temperature of the substrate 106 has been confirmed to be set at a given temperature by means of a heater 112, a high-frequency power source 113 set to the desired power is switched on to generate glow discharge in the reaction vessel.
During the formation of the deposited film, the substrate 106 is rotated at a constant speed by means of a motor 114 to form a deposited film uniformly. In this way the amorphous silicon deposited film can be formed on the substrate 106.
However, in such a method for manufacturing an electrophotographic photosensitive member, there is a region in which the deposited film is formed at a higher rate, and hence it is difficult to constantly stably obtain at a high yield a deposited film having a uniform film quality, satisfying requirements for optical and electrical characteristics and also giving a higher image quality when images are formed by electrophotography. This is a problem remaining unsettled.
Namely, the electrophotographic photosensitive member prepared by the method of manufacturing an electrophotographic photosensitive member, comprising the step of forming on a metal substrate a non-monocrystalline deposited film such as the amorphous silicon deposited film by plasma CVD, often causes density unevenness and spots on an image which are not removable even at optimized conditions for the formation of the deposited film.
Hitherto, since copies have been made mainly for the purpose of copying originals printed or written exclusively in type (what is called line copying), such unevenness and spots have not been questioned. However, with a recent improvement in the quality of images formed by copying machines, originals containing halftones as in photographs have been copied and such unevenness and spots have been questioned. In particular, in the case of full-color copying machines recently having come into wide use, such unevenness and spots result in unevenness of colors which becomes visually more apparent, and hence has become very important.
These changes of the substrate surface are so minute that they can not be detected even if the conductivity is measured by attaching electrodes at the upper part. When, however, charging, exposure and development are carried out by electrophotography using such an electrophotographic photosensitive member, in particular, when a uniform image is formed in halftone, even a small difference in potential on the surface of the electrophotographic photosensitive member results in unevenness of image density, and comes to be visually recognizable.
In addition, the plasma CVD in which a starting material gas is decomposed by microwave glow discharge, i.e., microwave plasma CVD, has recantly attracted notice on an industrial scale as a method of forming deposited films.
The microwave plasma CVD is advantageous over other processes because of its higher deposition rate and a higher efficiency of starting material gas utilization. U.S. Pat. No. 4,504,518 discloses an example of the microwave plasma CVD making the most of such advantages. The technique disclosed in this patent is a technique in which a deposited film with a good quality is obtained at a high deposition rate by microwave plasma CVD at a low pressure of 0.1 torr or less.
Japanese Patent Application Laid-open No. 60-186849 also discloses a technique by which a starting material gas can be utilized at a higher efficiency by microwave plasma CVD. The technique disclosed in this, publication is, in summary, a technique in which substrates are so arranged that they surround a microwave energy introducing means to form an internal chamber, i.e., a discharge space, thereby greatly improving the efficiency of starting material gas utilization.
Japanese Patent Application Laid-open No. 61-283116 also discloses an improved microwave technique for producing a semiconductor member. More specifically, this publication discloses a technique in which an electrode (a bias electrode) is provided in the discharge space as a plasma potential controller, and the desired voltage (a bias voltage) is applied to this bias electrode to form a deposited film while controlling ion bombardment against the deposited film, thereby improving the characteristics of the deposited film. An electrophotographic photosensitive member prepared by such microwave plasma CVD, however, often is a serious cause of the aforesaid problems.
On the other hand, none of such image density unevenness and spots occur in electrophotographic photosensitive members prepared by processes other than the microwave plasma CVD, i.e., selenium electrophotographic photosensitive members prepared by vacuum deposition, OPC electrophotographic photosensitive members prepared by blade coating or dipping, even with use of the substrate having been cleaned by the process previously described.
Even in devices prepared by plasma CVD, none of the above problems also occur in device since a delicate positional difference on the substrate does not affect their performances as, for example in solar cells.